i cant delete unwanted storage on my iphone

Use internet speed over 15 Mbps (both download and upload) speed for error free update. Avoid latching on to Hotspot or WiFi Extenders

VPN or proxy connections might prevent your device from contacting the update servers.

• Get help with over-the-air iOS updates - Apple Support

• Remove and download the iOS update again

If you still can't install the latest version of iOS, try downloading the update again:

1. Go to Settings > General > [Device name] Storage.

1. Find the iOS update in the list of apps.

1. Tap the iOS update, then tap Delete Update.

1. Go to Settings > General > Software Update and download the latest iOS update.

If you don’t see the update in the list of apps or if the issue happens again, you need to update your device with iTunes.

Try updating iOS after each step.

• Try Forget the WiFi network and add again

• Try another WiFi network 

• Toggle sets automatically off and then on

• Reset your network settings

• Force restart your device

• Remove any beta profiles, if applicable

• If everything fails: - Use iTunes or Finder (for MacOS Catalina+) to update your device instead of over-the-air

• Get help with iOS update and restore errors - Apple Support

• If you see an error when you update or restore your iPhone, iPad

You cannot increase storage of an iPhone. However, you can optimize iPhone Storage by using iCloud Storage. Save space on your device

Settings > [your name] > iCloud Tap Photos > Choose Optimize [device] Storage Set up and use iCloud Photos - Apple Support

You can buy iCloud Storage. --> Buy more iCloud storage - Apple Support

You can manage your storage --> How to check the storage on your iPhone, iPad, and iPod touch

Manage your Storage --> Manage your photo and video storage - Apple Support

Your photos are always available for both iPhone and iCloud. You delete it on the iPhone it is gone from iCloud and vice-versa. To save space on your iPhone use optimized iPhone storage. Remember, if you delete in one it is deleted everywhere.

Get started with iCloud Photos:

1. Tap Settings > [your name] > iCloud > Photos.

1. Turn on iCloud Photos.

1. Select Optimize iPhone Storage to save space on your device.

With Optimize Storage, smaller, space-saving photos and videos are kept on your device while all of your original, full-resolution versions are stored in iCloud. And as long as you have enough space in iCloud, you can store as many photos and videos as you want.

How to check the storage on your iPhone, iPad, and iPod touch